Various measures for reduction of emissions of CO2 are being adopted in order to deal with atmospheric pollution and global warming. In the automobile industry, the reduction of emissions of CO2 is highly expected in association with the spread of electric vehicles and hybrid electric vehicles. Thus, development of high-performance secondary batteries used as driving power sources of motors for these vehicles is actively being carried out.
In particular, a higher capacity and cycle property are required for the secondary batteries used as driving power sources of motors for those vehicles. In view of this, lithium ion secondary batteries having high theoretical energy are gaining increasing attention among other types of secondary batteries.
The lithium ion secondary batteries are required to store a large amount of electricity in positive electrodes and negative electrodes per unit mass, in order to increase energy density of the lithium ion secondary batteries. Thus, it is quite important for the lithium ion secondary batteries to determine appropriate active materials used in the respective electrodes so as to fulfill such a requirement.
For example, Japanese Unexamined Patent Application Publication No. 2004-311429 has proposed an electrode material and an electrode structure capable of improving performance of a lithium ion secondary battery with low resistivity, high efficiency of charge and discharge, and high capacity. Patent Literature 1 has further proposed a secondary battery using the electrode material and the electrode structure.
In particular, Japanese Unexamined Patent Application Publication No. 2004-311429 discloses an electrode material including solid-state alloy particles mainly containing silicon, in which a microcrystalline or amorphous substance containing an element other than silicon is dispersed in microcrystalline silicon or amorphous silicon.